The present invention relates to cylinder locks, of the type comprising:
a fixed lock body or stator, having a cylindrical cavity,
a cylinder or rotor, rotatably mounted within the cylindrical cavity of the fixed body and having an axial passage for receiving a key,
a plurality of locking tumblers slidably mounted within radial holes of the rotatable cylinder, opening on said axial passage, said tumblers being adapted to be engaged at one end thereof by a key having a predetermined profile in order to arrange themselves in a position in which they enable a free rotation of the rotatable cylinder within the fixed body,
a plurality of counter-tumblers, slidably mounted within holes which are formed in the fixed body of the lock and open on the cylindrical cavity of said fixed body, said holes for the counter-tumblers being adapted to become aligned with the holes for the tumblers in the rotatable cylinder at a given angular position of the latter, and
means for biassing the tumblers radially towards the axis of the rotatable cylinder when the latter is at said given angular position.
In the conventional locks of the above indicated type, the above mentioned biassing means are constituted by coil springs arranged within the holes of the fixed body wherein the counter-tumblers are movable, so as to push the counter-tumblers against the respective tumblers, towards the axis of the rotatable cylinder. These locks enable a burgler to determine the profile of the key which can open the lock, by inserting a tool within the key hole and pushing the tips of the lock tumblers by this tool, against the action of the above mentioned coil springs.
The object of the present invention is that of proposing a new type of lock which has a higher degree of safety with respect to the conventional locks of the above indicated type.
In view of achieving this object, the invention provides a lock having all the above mentioned features and further characterized in that in the case of at least one of said tumblers the means for biassing this tumbler radially towards the axis of the rotatable cylinder are magnetically operative biassing means, which comprise a first permanent magnet arranged within the hole in the fixed body where the respective counter-tumbler is movable and a second permanent magnet associated with said key and adapted to draw the first permanent magnet towards the axis of the rotatable cylinder when the key is received within the rotatable cylinder, so that the first permanent magnet biasses the respective tumbler against the key.
Naturally, it is possible to provide one or more tumblers of the lock and, if desired, even all the tumblers of the lock, with magnetically operative biassing means.
According to a first solution, the above mentioned first permanent magnet is arranged within the respective hole of the fixed body between the respective counter-tumbler and an end wall of the hole. Alternatively, the first permanent magnet may be arranged within the respective hole of the fixed body between the respective counter-tumbler and the respective tumbler.
In order to improve the magnetic efficiency, preferably the tumbler and/or the respective counter-tumbler are made of ferromagnetic material.
The second permanent magnet is fixed within a seat formed in the key on a surface opposite to that which is for cooperating with the tumblers of the rotatable cylinder.
In case at least one of the tumblers of the rotatable cylinder has biassing means of the conventional type constituted by a coil spring arranged within the hole of the respective counter-tumbler, according to the invention the counter-tumblers associated with magnetically operative biassing means have a greater length than the counter-tumbler associated with coil spring biassing means. In this manner, a lock of conventional type can be transformed into a lock according to the invention with no modification to the geometry of the fixed body.
In case said key has a flattened active portion and accordingly the above mentioned axial passage for the key has a similar shape, having a general plane perpendicular to a plane containing the axes of the radial holes of the rotatable cylinder, the above mentioned active portion of the key has a first face having cavities adapted to cooperate with the tips of the lock tumblers and an opposite face in which the seat for each second permanent magnet is formed.
Due to the above mentioned features, when the key is not introduced into the lock, the first permanent magnet is not biassed towards the axis of the rotatable cylinder. Therefore it is impossible for a non-authorized person to introduce a tool into the key axial passage and press this tool against the tip of the above mentioned tumbler in order to determine the profile of the key which can open the lock. Thus, the lock according to the invention has a higher degree of safety with respect to the known locks.